Structure of the human spliceosomal C complex. (A) Schematic of the PM5 pre-mRNA on which C complexes are assembled and the two steps of pre-mRNA splicing. Due to the absence of a 3′ splice site and 3′ exon, step 2 requires the addition of an exogenously added 3′ exon-containing oligonucleotide. The color code for exon 1 (green) and the two intron regions, 5′ splice site (blue) and anchoring site (red), is also used in Figures 3–7. (B) Class average of EM images showing the negatively stained C complex in the dominant view. (C) The six structural domains of the C complex according to Golas et al. (2010) are indicated on a schematic outline of the C complex (dominant view). (D) 3D reconstruction of the human C complex from cryo-EM images (Golas et al. 2010). The 3D structure is shown in an orientation corresponding to the dominant view.
